#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
using namespace std;

const int N = 1e6 + 10, INF = 0x3f3f3f3f;

int n, p;
int a[N];

void solve()
{
    cin >> n >> p;
    int r = 0;
    for (int i = 1;i <= n;i++) {
        cin >> a[i];
        if (a[i] == 0) r = i;
    }

    int ans = 0;
    if (p < r - 1) {
        while (p < r - 1 && p < n) {
            if (a[p + 1] == 1) { ans++;a[p + 1] = 0; }
            p++;
        }
    }
    int l = 0;a[n + 1] = 1;
    while (a[l + 1] == 1) l++;
    while (p >= l) {
        if (a[p] == 1 && p != l) { ans++;a[p] = 0; }
        if (a[p + 1] == 0) ans++;
        p--;
    }
    cout << ans << '\n';
}

signed main()
{
    //ios::sync_with_stdio(0);
    //cin.tie(0);cout.tie(0);
#define ONLINE_JUDGE
#ifndef ONLINE_JUDGE
    std::istringstream in(R"()");
    std::cin.rdbuf(in.rdbuf());
#endif
    int T = 1;
    //cin>>T;
    for (int i = 1;i <= T;i++) {
        solve();
    }
}